1. Field of the Invention
An aspect of the present invention relates to a reference voltage generation circuit having a desired temperature dependency and to a semiconductor storage apparatus using the reference voltage generation circuit.
2. Description of the Related Art
Conventional semiconductor apparatuses, more particularly, conventional semiconductor storage apparatuses having ferroelectric memory cells or the like employ reference voltage generation circuits having desired temperature dependencies (see, e.g., JP-2004-158087-A). Such a reference voltage generation circuit has a band gap reference (BGR) circuit that generates a constant voltage which has a temperature dependency and does not depend on a power supply voltage in a given voltage range.
Meanwhile, burn-in (acceleration) test is performed on semiconductor storage apparatuses to apply a high power supply voltage as one of reliability tests. Thus, it is necessary for reference voltage generation circuits to generate a voltage which increases depending on a power supply voltage that is equal to or higher than a given value (i.e., a burn-in start voltage).
The following method is considered as one means for achieving such an object. That is, according to this method, an apparatus is configured to have a first circuit for generating a constant voltage, which does not depend on a power supply voltage, and a second circuit for generating a burn-in voltage which rises in proportion to the power supply voltage. And, this apparatus is adapted to combine outputs of the first circuit and the second circuit, to output the constant voltage in a range of voltages which are equal to or lower than a burn-in start voltage, and to output the burn-in voltage in a range of voltages which are higher than the burn-in start voltage.
However, when such a method is applied to a conventional reference voltage generation circuit having a temperature dependency, a sufficient burn-in (acceleration) test cannot be performed in a normal operation assurance temperature range, because the second circuit does not have an appropriate temperature dependency. That is, in a case where the burn-in start voltage (e.g., 3.8 [V]) is set at the lower limit (e.g., −40° C.) of the normal operation assurance temperature range, the constant voltage output from the first circuit rises depending on a temperature which is equal to or higher than the burn-in start voltage. Accordingly, as the temperature rises, the burn-in start voltage rises. Thus, at a high temperature (e.g., 85° C.), an appropriate burn-in voltage cannot be generated. In a range of voltages which are equal to or lower than the upper limit (e.g., 4.5 [V]) of the power supply voltage, a reference voltage remains the constant voltage. Consequently, the burn-in (acceleration) test cannot be performed.